When silicon dots or nanoclusters are formed in a data storage portion of an integrated circuit, the nanoclusters that are deposited need to be preserved during subsequent processing. Typically, further processing often includes exposure to highly oxidizing ambients that can degrade or consume the nanocrystals. It is necessary to preserve the physical and electrical characteristics of nanocrystals during subsequent processing. A plasma nitridation of silicon dots has been proposed for long-term memory device retention time. However, the levels of nitrogen incorporated by nitridation of silicon are not high enough to serve as a robust oxidation barrier. Significant oxidation of the surface of a silicon dot makes the silicon dot very difficult to erase.
During deposition nanoclusters of differing sizes and shapes are formed. Some deposited nanoclusters are much larger than others while others are oblong in shape. Even with tight nanocluster processing control that results in a narrow dispersion of cluster sizes, the presence of a few substantially larger clusters in the peripheral area is not statistically insignificant. When nanoclusters are deposited on a thin oxide surface, a long wet etch or dry etch is required to remove those nanoclusters which are substantially larger than the mean size. Such a long wet etch or a dry etch will often compromise the integrity of devices built in the peripheral areas. For example, such etches will unintentionally remove portions of layers in the peripheral areas which are not desired or intended to be removed. A typical example is the recess of the trench isolation oxide and its concomitant problems. A long wet etch or dry etch therefore compromises the integrity of devices built in the peripheral areas. Selective removal of nanoclusters is therefore problematic.
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